The present invention relates to a method for measuring such volatile hydrides as diborane (B.sub.2 H.sub.6), arsine (AsH.sub.3), phosphine (PH.sub.3), stibine (SbH.sub.3), hydrogen selenide (SeH.sub.2), monosilane (SiH.sub.4) and the like which are broadly used as doping material or epitaxializer in the field of semiconductor industry.
Hitherto, the following methods for measuring volatile hydride concentration have been known (1) colorimetric methods (methods of chemical analysis) based primarily upon their reaction with reagents, (2) infrared methods utilizing the property of the gas molecule to be examined to absorb the infrared rays, (3) ultraviolet methods utilizing the property of the gas molecule to be examined to absorb ultraviolet rays, and (4) the atomic absorption method based on measuring the light absorption of an atomic molecule caused by thermal decomposition of the gas to be examined. However, colorimetric methods have weak points such as complicated and time consuming measuring operations. Both the infrared and the ultraviolet method both of them proved to have poor measurement sensitivity in that amounts as high as several ppm could only be measured with difficulty by these methods. The atomic absorption method was inconvenient in various ways for example, high temperature on the frame was unavoidable, apparatus was expensive and the like. As mentioned above, none of the hitherto known methods for measuring volatile hydrides could bring about a satisfactory result. Further, measurement of extremely small quantities of hydrides was considered extremely difficult or almost impossible. These compounds are strongly toxic, the tolerance limit or allowable concentration is generally considered to be ranging between about 0.1 ppm. For example, the limit 0.05-0.3 ppm (50-300 ppb), for arsine is 0.05 ppm; and for phosphine it is 0.3 ppm for stibine it is 0.1 ppm for hydrogen selenide it is 0.05 ppm; and for diboran 0.1. Detection and accurate measurement of these compounds were difficult. Especially diborane had been considered to be almost impossible to measure. In view of the fact that volatile hydrides are broadly used these days, the above situation was not desirable for health maintenance reasons.